2020 Physics: Fundamental Forces:  Electricity and Magnetism

PH.PS2.4 Use mathematical representations of Newton’s Law of Gravitation and Coulomb’s Law to describe and predict the gravitational and electrostatic forces between objects.*

PH.PS2.5 Plan and conduct an investigation to provide evidence that an electric current can cause a magnetic field and that a changing magnetic field can cause an electric current.

PH.PS3.5 Develop and use a model of two objects interacting through electric or magnetic fields to illustrate the forces between objects and the changes in energy of the objects due to the interaction.

(Note: Only Coulomb’s Law and electrostatic forces are addressed in this bundle. Newton’s Law of Gravitation and gravitational forces are addressed in the “Forces and Motion” bundle.)

In a Nutshell

Students use Coulomb’s law to mathematically describe and predict the effect of electrostatic forces between objects. These forces are explained by different types of fields (electric, and magnetic) that exist in the space around these objects. Students investigate the relationships between electric currents, magnets, and magnetic fields. Using provided materials students plan and conduct investigations to provide evidence that magnets or electric currents can cause magnetic fields, and electric charges or changing magnetic fields can cause electric fields. Student-developed models can be used to represent the patterns in electric and magnetic fields around objects and predict the effect of the interaction of the fields of two objects on the forces between them and their energy. Students use a model to illustrate that when objects interact in a field the energy stored in the field changes when the objects change their relative position in the field.

Student Actions

Teacher Actions 

• Use mathematical representations of Coulomb’s law to describe the patterns (distance and charge) that affect electrostatic force between two objects.

• Use mathematical representations to predict the electrostatic force between two objects in a system.

• Plan and conduct an investigation to provide evidence that an electric current causes a magnetic field.

• Plan and conduct an investigation to provide evidence that a changing magnetic field causes an electric current.

• Use evidence from investigations and models to explain that both electric and magnetic forces between objects are explained by fields which permeate and can transfer energy through space. 

• Develop a model to describe the relationships between force, energy, and relative position for two objects interacting through electric or magnetic fields.

• Use a model to predict how changing relative position between objects interacting through electric and magnetic fields affects force between object and energy stored in the system. 

• Support students in the use of mathematical representations to describe and predict that the electrostatic force is directly dependent upon the charge of two objects.

• Support students in the use of mathematical representations to describe and predict that the electrostatic force is inversely proportional to the square of the distance that separates the center of charged objects.

• Support students in planning investigations that produce evidence for the relationship between electric current and magnetic fields.

• Provide materials students can use to conduct investigations that produce evidence for the relationship between electric current and magnetic fields.

• Assist students in using data from investigations to explain that both electric and magnetic forces between objects are explained by fields which permeate and can transfer energy through space.

• Provide tasks for students to develop models to describe the relationships between force, energy, and relative position for two objects interacting through electric or magnetic fields.

• Assist students in using models to predict how changing relative position between objects interacting through electric and magnetic fields affects force between object and energy stored in the system. 

Key Concepts 

Misconceptions 

Types of Interactions 

• Newton’s Law of Universal Gravitation and Coulomb’s Law provide the mathematical models to describe and predict the effects of gravitational and electrostatic forces between distant objects.

• Forces at a distance are explained by fields (gravitational, electric, and magnetic) permeating space that can transfer energy through space.

• Magnets or electric fields cause magnetic fields; electric charges or changing magnetic fields cause electric fields.

Definitions of Energy

• "Electrical energy" may mean energy stored in a battery or energy transmitted by electric currents.

Relationship Between Energy and Forces

• When two objects interact, each one exerts a force on the other. These forces can transfer energy between the objects. Forces between two objects at a distance are explained by force fields (gravitational, electric, or magnetic) between them. 

• Gravitational forces are stronger than electrostatic forces between charged particles.

• ­In a two-object system, the more massive object (or object with the greater charge) exerts a greater force on the other object.

• ­Static magnetic fields produce electric currents.

• Energy is not transferred from one object to another unless those objects are in direct contact with one another.  

• Energy can be transformed into a force.

• Electric fields are the same as magnetic fields.  

• ­Objects always accelerate in the direction of electric field lines.

• ­Positively charged objects are attracted to the north pole of magnets and negatively charged objects are attracted to the south pole.

• ­A magnetic field only exists outside of the magnet. 

Instructional Resources 

Unit 3: Fundamental Forces - Electricity and Magnetism